In this work, liposomes are being used in lieu of the host cell to study membrane aspects of Sendai virus infection. When gangliosides are included in the composition of liposomes, they serve as Sendai virus receptors and cause the liposomes to envelop virus by circumferential ligand-receptor binding as in the ingestion phase of phagocytosis. Sendai virus membrane can fuse with liposomes, and they initiate this fusion at the leading edge of the envelopment process where there is a local region of very high curvature. After fusion, the virus disassembles so that the vira RNP is within the liposome and the viral glycoprotein spikes are distributed over the surface of the liposome. During the next year: (A) Membrane fusion will be quantitated by (1) using virus containing labeled proteins and assaying the counts resulting from the viral internal proteins within the liposomes after fusion, and by (2) assaying for viral kinase and transcriptase activities within the liposome. (B) The membrane properties that determine viral disassembly will be examined. Preliminary data suggest that some liposome compositions allow liposomes to fuse with the viral membrane without subsequent viral disassembly. If further data confirm this, the work will be extended to determine the mechanism of disassembly. (C) The role of membrane curvature in membrane fusion will be further investigated. Liposomes will be made with less negative charge to see if the primary role of curvature is to allow close approach of two negatively charged surfaces. To see what role surface energy plays in membrane fusion, the effect upon fusion of increasing the free energy by means other than increased curvature will be tested. (D) Whether virus containing F. protein can fuse with liposome will be determined.